Crude glyceride oils contain free fatty acids and other impurities. Such crude oil is refined by contacting the crude oil with aqueous alkali in a batch for continuous process. The alkali reacts with the free fatty acids to form soap. The soap and other solid impurities are separated from the oil by settling or centrifuging. The solids thus obtained are designed "soapstock" or "foots"; the soapstock is alkaline.
Fatty acids can be recovered from soapstock as a valuable byproduct of the oil refining process. A product high in fatty acid content (generally about 95% free fatty acids) is obtained from the soapstock by acidulation with a mineral acid such as sulfuric or hydrochloric acid. Soapstock is reacted with an aqueous acid solution at an elevated temperature. If the acidulated soapstock is allowed to settle, it separates into three layers. The bottom layer is an acidic aqueous solution which can be pumped off and recycled. The top layer is the desired fatty acid product which may be used as is (e.g., for animal feed), or may be further treated to obtain more highly purified fatty acids (e.g., by distillation). The middle layer is an emulsified sludge material, a semisolid, emulsified layer containing primarily gums (e.g. lecithins and other phospholipids), water, and a substantial quantity of the desired fatty acid product entrained therein.
A variety of batch and continuous processes for recovering fatty acid products from glyceride oil soapstocks are known. References disclosing such processes include the following U.S. Pat. Nos.: 2,230,196 issued to Clayton on Jan. 28, 1941; 2,239,131 issued to Thurman on Apr. 22, 1941; 2,472,193 issued to Clayton on June 7, 1949; 2,601,375 issued to Durkee on June 24, 1952; 2,812,343 issued to Cox & Brice on Nov. 5, 1957; 2,929,714 issued to Wittee & Sipos on Mar. 22, 1060; 2,970,910 issued to Thurman on Feb. 7, 1961; 3,425,938 issued to Bloomberg & Hutchins on Feb. 4, 1969; 3,428,660 issued to Morren on Feb. 18, 1969; 3,787,460 issued to Gadefaix & Klere on Jan. 22, 1974; 3,974,069 issued to Nettli on Aug. 10, 1976; 4,100,181 issued to Phillips & Leavens on July 11, 1978; 4,118,407 issued to Red & llagan on Oct. 3, 1978; and 4,361,517 issued to Duff & Segers on Nov. 30, 1982. Other references disclosing processes for continuous or batch acidulation of glyceride oil soapstocks include the following: Keith, F. W., V. G. Bell & F. H. Smith, "Continuous Purification and Acidulation of Vegetable Oil Soapstock", J. Am. Oil Chemists' Soc., Vol. 32 (October, 1955), pp. 517-519; Todd, D. B., and J. E. Morren, "Continuous Soapstock Acidulation", [J. Am. Oil Chemists' Soc., Vol. 42 (April, 1965), pp. 172A,178A; Braae, Ben, "Degumming & Refining Practices in Europe", J. Am. Oil Chemists' Soc., Vol. 53 (June 1976), pp. 353-357; Woerfel, J. B., "Alternatives for Processing of Soapstock", J. Am. Oil Chemists' Soc., Vol. 60 (February, 1983), pp. 262A-265A; and Mag, T. K., D. H. Green, & A. T. Kwong, "Continuous Acidulation of Soapstock & Recovery of Acid Oil", J. Am. Oil Chemists' Soc., Vol. 60 (May, 1983).
Morren discloses a process for continuous acidulation of soapstock and separation by centrifuging. Morren indicates that the acidulation reaction causes a tenacious interfacial emulsion which can be broken by heating and the addition of water. Most of the references cited hereinabove do not mention formation of a sludge layer between the fatty and aqueous layers, and therefore do not deal with disposal of the sludge layer.
In commercial soapstock acidulation processes, the sludge material is commonly retained with the fatty material initially. The sludge material is subsequently removed from the fatty layer by settling and is often discarded, because it has been found to be uneconomical to recover the fatty acid product entrained in the sludge material.